Intramedullar Osteosynthetic Device of Two Bone Parts, In Particular of the Hand and/or Foot

ABSTRACT

An intramedullar osteosynthetic device includes a body with an elongated shape and a flat cross-section having, in succession, from one of its ends, a first fixation zone cooperating with one of the bone parts to be immobilised, a median zone suitable for withstanding the shear and bending stresses, and a second fixation zone in the other bone part to be immobilised. Each of the fixation zones is made from a material suitable for enabling their deformation by thermal action (tepid memory) or mechanical action (superelasticity), to permit an introduction into the bone parts without pulpar approach, followed by a fixation in the bone parts, while avoiding any rotational movement, withstanding the tensile stresses, and maintaining a compressive force. At least one of the fixation zones has two tabs or fins and which are separable under the effect of the deformation.

The invention relates to the technical field of orthopaedic implants, particularly for arthrodeses and osteosyntheses.

It may be recalled that the object of an arthrodesis is to obtain very good stability both primary and secondary, and to place, or to maintain, in compression, two bone parts or bone fragments that should be consolidated. Stability is a critical factor for obtaining consolidation, while minimising the attendant problems such as pain, swelling, etc. The compressive action serves to consolidate the osteotomy more rapidly in the position selected by the surgeon during the operation.

Various technical solutions have been proposed for carrying out an arthrodesis, particularly in the foot, the hand, the wrist, etc. Mention can be made, for example, of basic staples without shape memory which do not produce a compression, as opposed to memory staples which serve to place the two bone parts to be consolidated in compression, which corresponds to the objective.

However, to obtain satisfactory stability, it is necessary to place two, or even three staples, in different planes. This increases the dimensions considerably, thereby limiting applications (metacarpo-phalangeal joint, for example).

Extramedullary plates and screws have also been proposed, requiring an alternatively large dimension. In this respect, their miniaturisation is difficult to conceive, because this could raise problems of strength and stiffness. Some types of screws can be used in intramedullary osteosynthesis, but they raise positioning difficulties (passage through the pad in particular).

Use can also be made of pins which have a smaller size. However, the stability obtained is unsatisfactory and it is necessary to withdraw them.

Intramedullary nails are also known, but they require supplementary stapling in order to prevent them from rotating.

It is the object of the invention to remedy these drawbacks simply, safely, effectively and efficiently.

The problem that the invention proposes to solve is to permit the fixation of two bone parts to one another, rigidly with dynamic and retentive compression, in order to obtain a reliable and rapid osteosynthesis.

To solve such a problem, an intramedullary arthrodesis element has been designed and developed which consists of a body with an elongated shape having, in succession, from one of its ends, a fixation zone cooperating with one of the bone parts to be immobilised, a median zone suitable for withstanding the shear and bending stresses, and a fixation zone in the other bone portion to be immobilised, each of the said fixation zones is profiled and made from a material suitable for enabling an introduction into the bone parts without pulpar approach, followed by a fixation in the said bone parts, while avoiding any rotational movement, withstanding the tensile stresses, and maintaining a compressive force.

The invention has a particularly advantageous application, which can however not be considered as limiting, for the preparation of arthrodesis in the proximal and median phalanges, for proximal interphalangeal joints and distal interphalangeal joints, in the hand and/or the foot.

To solve the problem of taking account of the anatomy, and particularly of the internal shrinkage of the bone, the median zone is linked to at least one of the fixation zones by a connecting zone.

To solve the problem of permitting the implant of the element followed by the compression of the bone fragments, the fixation zones are made from a shape memory material to be deformed by thermal and/or mechanical action.

To produce the fixation zones, which may be identical or not, various technical solutions are feasible, according in particular to the type of arthrodesis performed and the joints to be treated.

For example:

-   -   one of the fixation zones has two tabs or fins which are         separable under the action of the shape memory;     -   one of the fixation zones has a tab or rod which can be curved         under the action of the shape memory;     -   one of the fixation zones has, in its thickness, a slot for         permitting a deformation by elasticity, or memory, under the         action of the shape memory.

In one embodiment, the overall body has a flat cross-section.

The invention is described below in greater detail in conjunction with the figures of the drawings appended hereto in which:

FIG. 1 is a schematic plan view showing the placement of the intramedullary arthrodesis element of the invention between a proximal phalange and a median phalange to consolidate the proximal interphalangeal joint;

FIG. 2 is a plan view of an exemplary embodiment of the arthrodesis element at the time of its introduction;

FIG. 3 is a view corresponding to FIG. 2 showing the arthrodesis element after its implant to produce the compression;

FIG. 4 shows the placement of the element of the invention in a toe.

The arthrodesis element of the invention consists of an elongated body denoted as a whole by (1). Each of the ends of the body is conformed to produce a fixation zone (1 a) linked to a fixation zone (1 b).

Between the two fixation zones (1 a) and (1 b), at least one median zone (1 c) is formed capable of withstanding the shear and bending stresses. In general, the shear and bending stresses are applied to the bone site to be consolidated. The shape of this median zone (1 c) is adapted to the internal shape of the bone. Its length is determined in order to allow a slight offset in the centring.

For information, and in a non-limiting manner, this median zone may have a rectangular cross-section measuring about 2 to 3 mm×1 to 1.5 mm and a length of about 3 to 5 mm (for the foot and the hand).

The fixation zones (1 a) and (1 b) are conformed to avoid any rotational movement, withstand a tensile force, and maintain the manual compression applied at the time of the implant by the surgeon in order to reduce the site. To obtain this result, the fixation zones (1 a) and (1 b) are made from a shape memory material to be deformed by thermal action (tepid memory) of mechanical action (superelasticity). The goal, in the fixation zones, considering their profile on the one hand, and the type of material on the other, is to permit an introduction into the bone parts, particularly dorsally without pulpar approach, on the one hand, and to produce a fixation in the said bone portion in order to obtain or to maintain the desired compressive force, on the other. The fixation zones (1 a) and (1 b) are identical or not, according to the type of bone and its morphology.

Depending on the type of arthrodesis performed, that is, the type of interphalangeal joint to be consolidated for example, the fixation zones (1 a) and (1 b) may have different embodiments.

For example, one of the fixation zones (1 a) has two tabs or fins which are separable under a thermal action for example. Otherwise, these fixation zones (1 a) may have a single tab or rod which can be curved under the action of a memory of the component material. Otherwise, the fixation zone (1 b) has, in its thickness, a slot to permit deformation by elasticity, under a thermal action for example, and to maintain the position by pressing on the length of the bone.

According to another feature of the invention, to take account of the anatomy of the various phalanges for example, that is the internal shrinkage of the bone (hourglass shape), the median zone (1 c) is linked to at least one of the fixation zones (1 b) by a thinner connecting zone (1 d).

Reference can be made to the figures of the drawings which show an exemplary embodiment of an intramedullar arthrodesis element.

In this exemplary embodiment, the body (1) has, at one of its ends, a fixation zone (1 a) in the form of two tabs or fins (1 a 1)-(1 a 2). This fixation zone (1 a) is prolonged by a median zone, of generally substantially triangular shape in a plan view. The median zone (1 c) is connected to the other end fixation zone (1 b) by a connecting zone (1 d) having a generally rectangular shape in a plan view. The fixation zone (1 b) has, in its thickness, a slot of generally oblong shape (1 b 1).

Reference can be made to FIG. 2 which shows the element at the time of its introduction, that is before separation of the tabs (1 a 1) and (1 a 2), and the opening of the slot (1 b 1). For example, this configuration is obtained when the overall element is subject to a temperature much lower than that of the human body for example. Conversely, after the implant (FIG. 3), under the effect of the body heat, the tabs (1 a 1) and (1 a 2) are separated, in the same way as the slot (1 b 1), concomitantly causing a deformation of the fixation zone (1 b).

It should be noted that the profile of the median zone (1 c) prevents penetration when the site is reclosed.

In an alternative embodiment, the connecting zone (1 d) can be split to benefit from a swelling effect by shape memory and strengthening of the anchoring in the diaphyseal zone.

It should be recalled that the inventive element is ideal for the treatment of the onchogryphosis pathology, by performing an arthrodesis in the phalanges P1 and P2 on the radii 2 to 5, while observing that such applications must not be considered as limiting, by means of essentially dimensional adjustments (finger reimplants, arthrodesis of the distal interphalangeal joint and of the proximal interphalangeal joint of the hand, and the arthrodesis of the big toe).

Obviously, the entire arthrodesis element of the invention may have constructive features suitable for improving the fixation and compression in particular.

For example:

-   -   notches on the tabs on one of the sides for better fixation in         the ethmoid bone;     -   wavy tabs implanted (straight before implant) to permit         shortening and hence an additional compression of the         arthrodesis site compared with a simple fixation;     -   a tapered central zone to avoid undesirable penetration of the         implant at the time when the site is to be closed.

For information, the memory used is preferably a tepid memory, so that heating is unnecessary because of the lack of access. The opening begins at above 15 to 20° C., while the end takes place at about 30 to 35° C.

The operating technique remains conventional. 

1. Intramedullar osteosynthetic device for fixation of two bone parts to one another at a fracture site, comprising a body with an elongated shape and a flat cross-section having, in succession, from one end, a first fixation zone cooperating with one of the bone parts, a median zone suitable for withstanding shear and bending stresses, and a second fixation zone in an other bone part, each of the first fixation zones and the second fixation zone being made from a material enabling deformation by thermal action or mechanical action, to permit an introduction into the bone parts without pulpar approach, followed by a fixation in the bone parts, while avoiding any rotational movement, withstanding tensile stresses, and maintaining a compressive force, at least the first fixation zones having two tabs or fins and separable under effect of the deformation.
 2. Device according to claim 1, wherein the median zone is linked to the second fixation zone by a smaller section connecting zone.
 3. Device according to claim 1, wherein the first fixation zones and the second fixation zone are identical or not.
 4. Device according to claim 1, wherein the material is a material with a shape memory.
 5. Device according to claim 4, wherein at least one of the first and second fixation zones has a tab or rod which can be curved under action of the shape memory.
 6. Device according to claim 4, wherein at least the second fixation zones has, in its thickness, a slot for permitting a deformation by elasticity under action of the shape memory and a fixation by swelling.
 7. Device according to claim 1, wherein the median zone is profiled to avoid penetration when the fracture site is consolidated.
 8. Device according to claim 1, wherein the two bone parts comprise bone parts of a hand and/or foot.
 8. Device according to claim 1, wherein said material exhibits tepid memory and/or superelasticity. 